1. Field of the Invention
This invention is concerned broadly with petroleum oils such as: ordinary atmospheric and vacuum residua; the substantially nondistillable fractions of oil or solids derived from other petroliferous sources such as oil shale and tar sands; and with other naturally occurring heavy oils which are not amenable to atmospheric pressure distillation without substantial decomposition. In particular, this invention is concerned with the treatment of such a nonvolatile oil to convert a substantial fraction of it to volatile hydrocarbons, and simultaneously to convert the remaining residual fraction to an oil more amenable to upgrading than the untreated, original nonvolatile oil.
2. Prior Art
Commercial petroleum crude oils usually are distilled to recover light fractions which are useful, either with or without further processing, as gasoline, naphtha, kerosine, heating oil and the like. During the distillation, a gas oil fraction boiling from about 415.degree. F. (213.degree. C.) to about 650.degree. F. (340.degree. C.) may sometimes be recovered, and this fraction is used for catalytic cracking to form high grade gasoline and fuel oil. A general treatment of commercial distillation practice is found in "Petroleum Refinery Engineering" by W. L. Nelson, 4th ed., McGraw-Hill Book Company, Inc., New York, N.Y., 1958, in Chapter VII, pages 226-262, which text is incorporated herein by reference in order to furnish background material.
In general, petroleum oils distilled at atmospheric pressure undergo fairly extensive and undesirable decomposition when the distillation temperature exceeds about 680.degree. F. (300.degree. C.). For this reason, atmospheric pressure distillations are conducted to a cut point of about 650.degree. F. (340.degree. C.) for the heaviest volatile fraction, everything distilling above about 650.degree. F. (340.degree. C.) forming a so-called atmospheric residuum. This residuum, and similar oils which cannot be distilled at atmospheric pressure without undergoing some thermal cracking, are herein characterized as "substantially nonvolatile." In general, a residual oil is composed of fairly high molecular weight material of very complex chemical character, and contains a large portion of the total nitrogen and sulfur of the whole crude. It also contains all of the metals in the crude. Because of its nature, the residual fraction is generally considered of low value and may be disposed of as bunker fuel for ships, for example. In some refineries, the residual oil is distilled under vacuum to reduce its volume somewhat and recover a vacuum gas oil which may be blended or processed further. In other instances, a portion or all of the residuum may be pyrolyzed (i.e. coked) to recover a coker gas oil and a solid coke which may be marketed or used as fuel. None of these alternative uses for residual oil is particularly attractive economically, and for this reason considerable research has been done to discover ways to convert residual oil to gasoline and fuel oil. As a first step toward such goal, it has been proposed that the residual oil be demetallized and desulfurized, as exemplified by U.S. Pat. Nos. 3,891,541 to Oleck et al; 3,985,643 to Milstein; and 4,016,067 to Fischer et al. The entire contents of these patents are incorporated herein by reference. This demetallized and desulfurized residual oil is amenable to catalytic cracking or hydrocracking, thereby converting it to gasoline and fuel oil. However, because of the relatively refractory nature of the residual oil, the removal of metals and other contaminants requires high capital investment and operating costs. In brief, it appears that there is still a need for improved processes to convert residual oils to lighter fractions in the gasoline or light fuel oil boiling ranges.
Although the foregoing brief description has been couched in terms of current refinery practice and currently available crude oils, there are naturally occurring heavy oils which today are not produced and processed because it is uneconomic to do so. Such oils may be largely or totally substantially nonvolatile in the sense that that term is used herein. It is contemplated that improved processes such as that described herein pertaining to commercial residual oils would be applicable to such heavy oils.
It is an object of this invention to provide a process whereby a significant portion of a substantially nonvolatile petroleum oil such as a vacuum residuum may be converted to volatile hydrocarbons. It is a further object of this invention to provide a process for upgrading a substantially nonvolatile petroleum oil. It is a further object of this invention to provide a process for reducing simultaneously the amount and the average molecular weight of a substantially nonvolatile petroleum oil with the concurrent formation of a volatile hydrocarbon oil fraction. These and other objects will become evident on reading this entire specification including the claims hereof.
Attention is called to U.S. Pat. No. 3,506,731 issued Apr. 14, 1970 wherein is contained a description of the cracking of paraffins in the presence of aromatic hydrocarbons with mordenite catalyst, with the simultaneous formation of alkyl aromatics. Attention also is called to a publication by A. M. McAfee, Ind. Eng. Chem. 7, p. 737 (1915) in which is described the cracking of gas oil at 550.degree. F. and atmospheric pressure.